The present invention relates generally to relief valves and, more particularly, to a uniquely configured silencer system which is specifically adapted to accommodate thermal expansion displacements that may occur in piping systems through which high-pressure fluid is vented. The silencer system is configured to facilitate a reduction in unwanted noise created by the flow of the fluid by eliminating noise-generating sources created by the flow.
Vent silencers have been employed in various industries to muffle high velocity air or gas, including steam, which is flowing or venting to the atmosphere. For example, vent silencers are often used in conjunction with pressure relief valves or safety valves of the type utilized in high-pressure, high temperature steam service for relieving over-pressure from steam generating equipment. In this regard, it is not uncommon for the discharge from such high capacity safety valves to achieve sonic or near sonic velocity in the vent stack leading to the atmosphere such that the vent stack transmits the noise created at the safety valve as well as the noise generated as a result of the discharge of the flow to the atmosphere.
Various federal regulations have been created which stringently regulate the noise level that may be generated by such discharging safety valves. As a result, there has been developed in the prior art various types of silencer systems which are adapted to muffle a sonic gas, steam, or air stream. In the prior art, silencer systems are often used in an approach known as the “path treatment” of noise. In the path treatment approach, noise-generation is allowed to take place, with the noise-absorbing elements of the silencer systems being operative only to absorb the noise that has already physically been generated.
An alternative approach to noise reduction is known as “source treatment”. The source treatment approach relies on reducing the strength of the source of noise by various means including the control or reduction of fluid velocity. Source treatment applications may include wire meshes, metal foam, or equivalents that are placed into the flow path of the gas, steam or air jet in such a way that noise-generating mechanisms are weakened to a point wherein a high degree of noise reduction is achieved.
Prior art silencer systems have incorporated the path treatment approach for achieving noise reduction utilizing noise-absorbing elements to absorb noise that has been generated. One such prior art silencer system utilized for safety valves includes a vent stack that is connected to a drip pan. The vent stack is typically connected to the drip pan in a manner wherein an air gap separates the vent stack from the drip pan. The air gap is usually located near the safety valve which is usually positioned at a level that is easily accessible to plant personnel.
The drip pan provides a measure of corrosion protection for upstream components by collecting condensation as well as accumulations of melted snow and rain that may enter the vent stack. The drip pan also allows for a limited amount of relative movement between the vent stack and the drip pan due to thermal expansion. Thermal expansion of the silencer system occurs due to the flow of the high-pressure, high temperature fluid through the silencer system. Such thermal expansion creates excessive bending moments and deflective forces at an inlet to the silencer system. The drip pan silencer system is configured to absorb thermal growth motions in order minimize excessive stresses such that the useful life of the silencer system may be extended.
Unfortunately, drip pan silencer systems include inherent safety risks to plant personnel due to steam “blowback” through the air gap during conditions of high flow through the vent stack wherein excessive back pressure in the vent stack may cause high-temperature steam to escape through the air gap. Furthermore, the air gap may expose nearby plant personnel and expensive equipment to the risk of harm from excessive noise escaping through the air gap.
The present invention addresses these deficiencies by providing a silencer system which falls within the source treatment category and which may additionally be configured to include elements falling into the path treatment category. Additionally, the silencer system of the present invention is configured such that the risk of harm to personnel and equipment from high-temperature steam and excessive noise is minimized. Furthermore, the reduction in noise effected by the silencer system of the present invention may eliminate the need for costly vent stack insulation as well permit the use of smaller, more economical silencer system piping. Finally, the silencer system of the present invention may eliminate noise-generating sources created by fluid flowing from the relief valve such that the need for additional downstream silencing equipment may be reduced with a resulting savings in direct costs of the silencing equipment as well as the associated indirect costs of installing the equipment.